rod / räd/ • n. 1. a thin straight bar, esp. of wood or metal. ∎  a wand or staff as a symbol of office, authority, or power. ∎  a slender straight stick or shoot growing on or cut from a tree or bush. ∎  a stick used for caning or flogging. ∎  (the rod) the use of such a stick as punishment: if you'd been my daughter, you'd have felt the rod. ∎ vulgar slang a penis.2. a fishing rod.3. hist. a linear measure, esp. for land, equal to 5¹/₂ yards (approx. 5.029 m). ∎  (also square rod) a square measure, esp. for land, equal to 160th of an acre or 30¹/₄ square yards (approx. 25.29 sq m).4. inf. a pistol or revolver.5. Anat. a light-sensitive cell of one of the two types present in large numbers in the retina of the eye, responsible mainly for monochrome vision in poor light. Compare with cone (sense 3).PHRASES: ride the rods steal rides on freight trains: hundreds of young men took to riding the rods in search of employment.rule someone or something with a rod of iron control or govern someone or something very strictly or harshly.DERIVATIVES: rod·less adj.rod·let / -lət/ n.rod·like / -ˌlīk/ adj.

rod In the retina of the vertebrate eye, the more common of the two types of light receptor (compare CONE), which is sensitive to very low levels of stimulation. Many rods (in humans about 150) are connected by bipolar cells to a single ganglion cell whose axon is a nerve fibre in the optic tract; stimuli to the rods are summated (i.e. added together) to produce a total stimulus that must exceed a threshold before an impulse is discharged by the ganglion cell. Because the contribution of many individual rods is summated to produce a single impulse the resulting perceived image is not clearly defined. There are estimated to be about 65 × 10⁶ rods in a single human retina and the eyes of some animals (e.g. opossums) have retinas containing only rods and no cones.

rod A type of light-sensitive receptor cell present in the retinas of vertebrates. Rods contain the pigment rhodopsin and are essential for vision in dim light. They are not evenly distributed on the retina, being absent in the fovea and occupying all of the retinal margin. See also dark adaptation. Compare cone.

rod (rod) n. one of the two types of light-sensitive cells in the retina of the eye (compare cone). Rods are necessary for seeing in dim light. They contain the pigment rhodopsin, which is bleached in the light and regenerated in the dark. When all the pigment is bleached (i.e. in bright light) the rods no longer function. See also dark adaptation, light adaptation.

rod a thin straight bar, especially of wood or metal. In former British usage, a rod was a unit of measurement, the equivalent of a perch.
make a rod for one's own back do something likely to cause difficulties for oneself later.
rule with a rod of iron control or govern very strictly or harshly.
spare the rod and spoil the child if children are not physically punished when they do wrong their personal development will suffer. It is proverbial, from the early 11th century, and often with biblical allusion to Proverbs 13:24.